CO 233 denial code

Claim adjustment reason code 233. Often reported as CO 233.

Hospital-acquired condition or error

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 233 means

Charges were adjusted because they relate to treating a hospital-acquired condition or a preventable medical error.

Payers often refuse to pay for extra care caused by a condition the patient picked up in the hospital or by a preventable error, such as some falls, infections or wrong-site procedures.

With group code CO the facility normally absorbs the cost. Present on admission indicators and diagnosis coding drive most of these adjustments.

Group codes seen with 233

On a remittance, 233 comes after a group code. These are the ones it is most often reported with:

• CO 233 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• A condition was coded as not present on admission and is on the payer's hospital-acquired list.
• The present on admission indicator was missing or entered wrong.
• A serious preventable event occurred during the stay.

What to do next

1. Review the present on admission indicators against the record.
2. Correct and resubmit if the condition was present when the patient arrived.
3. Send the case to quality and compliance teams if a preventable event occurred.

Related codes

• 50 (reason code) Not medically necessary per the payer
• 16 (reason code) Missing information or billing error